Strain-promoted cycloadditions involving nitrones and alkynes—rapid tunable reactions for bioorthogonal labeling

Click Chemistry in Complex Mixtures: Bioorthogonal Bioconjugation

“…Strain-promoted alkyne-nitrone cycloaddition (SPANC) reactions demonstrate rate constants up to 60 M −1 s −1 (McKay et al, 2012; McKay et al, 2010; Ning et al, 2010), and have been used for N -terminal peptide modification (Ning et al, 2010), direct protein labeling, and pre-targeted labeling of ligand-receptor interactions on cell surfaces (McKay et al, 2011). Cyclic nitrones display greater stability toward hydrolysis and faster kinetics than their acyclic counterparts, and nitrone reactivity is tunable to allow for simultaneous SPANC reactions for multiplex labeling (MacKenzie and Pezacki, 2014; MacKenzie et al, 2014). Nitrile oxides have also been explored as alternative 1,3-dipoles in reactions with cyclooctynes to yield isoxazoles, and the reaction has been applied for generating oxime containing nucleotides and peptides (Jawalekar et al, 2011) as well as carbohydrates (Sanders et al, 2011).…”

Cycloadditions of Trans‐Cyclooctenes and Nitrones as Tools for Bioorthogonal Labelling

“…Where initial SPAAC proceeded with rate constants of 10 −2 m −1 s −1 , rate constants now exceed 10 −1 m −1 s −1 through the development of cyclooctyne analogues such as DIBO, DIFO, and BARAC . Alternative dipoles have also been investigated in these reactions, such as the strain‐promoted alkyne–nitrone cycloaddition (SPANC), which has been shown to demonstrate faster kinetics than the parallel reaction with azides, achieving rate constants of 1–10 2 m −1 s −1 . Nevertheless, new reactions are still urgently needed to expand the ability to perform modular and multiplex ligation reactions.…”

“…[9,10] Alternative dipoles have also been investigated in these reactions, such as the strain-promoted alkyne-nitrone cycloaddition (SPANC), which has been shown to demonstrate faster kinetics than the parallel reaction with azides, achieving rate constants of 1-10 2 m À1 s À1 . [11][12][13] Nevertheless, new reactions are still urgently needed to expand the ability to perform modular and multiplex ligation reactions.…”

Copper‐Free Postsynthetic Labeling of Nucleic Acids by Means of Bioorthogonal Reactions

“…Since then, numerous applications of SPAAC in biology, biomedical research, drug design, material science, and biotechnology have been reported, both in vitro—for determination of DNA modifications,34 for example—and in vivo, including in zebrafish35 and mice 36. In this regard, the ring strain of cyclooctynes has been tuned in order to develop suitable and powerful dipolarophiles for cycloaddition reactions not only with azide as a unique dipole in modified (bio)molecules,37 but also with nitrile‐oxide‐ or nitrone‐modified (bio)molecules,38 and fluorescent dyes 39. This goal has been achieved by introduction of an electron‐withdrawing group (difluorinated cyclooctyne; see 10 , Scheme ),40 by dibenzoannulation (dibenzocyclooctyne; see 11 ),41 by fusion with cyclopropane (bicyclo[6.1.0]nonyne; see 12 ),41 by increasing sp 2 hybridization into the ring parent (dibenzoazacyclooctynes; see 13 and 14 ),42 and by the introduction of sulfur atoms in a smaller ring (tetramethylthiacycloheptyne; see 15 ) 43.…”